Cross-coupling errors of micromachined gyroscopes

A model is developed for the response of a micromachined, rotary gyroscope subject to a general input motion. The governing equations are formulated for weakly nonlinear oscillations of the rotor, suspended above the moving substrate via elastic beams. The method of multiple scales is used to separate the slow and fast responses. This approach allows quick computation of the long-term behavior of the rotor without the need to integrate over fast oscillations. The power of the model to evince cross-coupling errors is demonstrated through examples.     

一种双自由度双级解耦微机械陀螺的特性分析

为了降低微机械陀螺的机械耦合和改善工作稳定性,提出了一种新颖的双自由度双级解耦微机械陀螺.建立并求解了该陀螺的动力学方程,并从理论上分析了陀螺的系统特性.利用数值求解工具MATLAB模拟了陀螺的幅频特性,结果表明当品质因子从50变化到1 000时,平坦区带的幅度和相位变化很小.理论和模拟均证实了该陀螺在选择适当的工作区带时,能获得较高的工作稳定性.     

Process window of micromachined gyroscopes subjected to vibrational frequencies

A micromachined gyroscope (or gyro) is used to measure angular velocities for many applications such as automotive, robotics, navigation, military and consumer electronics applications. For our specific automotive applications, the gyro is used to sense the yaw, roll, and pitch angular rates for ride stabilization and rollover detection. The process window is very important to the goal of achieving high volume mass production and cost reduction of the devices. The purpose of this study is to perform modal analyses, validate the simulation results with testing data, and provide a design tool for quick gyro element resonant frequency predictions. Then the process window and design limit can be quickly evaluated and optimized before the final wafers are built.     

Transition interface for improving the temperature characteristics of micromachined gyroscopes

This paper reports a method for improving the temperature performance of micromachined gyroscopes by using a transition interface between the sensitive structure and the vacuumed package. We analyzed the effect of transition interface on the thermal stress of the micromachined gyroscopes. The temperature dependence of the static capacitance, resonant frequency and zero output were experimentally studied over the range ?40 to 60 °C. A micromachined gyroscope suspended by a slanted beam was adopted in the experiment. In order to identify how the factors affect the temperature performance of the micromachined gyroscope, two types of the introduced gyroscopes were characterized. One was the original gyroscope having no transition interface, and the other was using 2 mm silicon as the transition interface. In contrast to the original gyroscope having no transition interface, the static capacitance and resonant frequency of the gyroscope adopting transition interface had a smaller temperature coefficient, especially for the static capacitance which has more than an order of magnitude improvement. As a result, the bias instability of the gyroscope improved to a higher level over temperature variations. It would provide a convenient and practical method for improving the temperature performance of micromachined gyroscopes.     

Effect of die attachment on key dynamical parameters of micromachined gyroscopes

This paper presents the effect of die attachment on the resonant frequency and quality factor of micromachined gyroscopes. Two types of epoxy die attachments are adopted in micromachined gyroscopes. A fourth order mass-spring-damper system is proposed to augment the dynamics of micromachined gyroscopes. Frequency response tests are implemented to analyze the quality factor and resonant frequency. Both maximums of the resonant frequency and quality factor are obviously much larger in the drive mode and sense mode when the more rigid die attachment is applied, due to the fact that rigid die attachment can minimize the energy loss through die substrate. Furthermore, the temperature dependence of the quality factor and resonant frequency on the die attachment is experimentally studied over the range −40°C to 60°C. Based on the experimental study, the rigidity, viscosity and temperature characteristics are the most considerable parameters for the die attachment in micromachined vibratory gyroscopes. Besides, the type of the mode shape is another factor determining the quality factor and temperature coefficient of resonant frequency. Balanced anti-phase mode operation can suppress the effect of die attachment.     

控制力矩陀螺框架伺服系统期望补偿自适应鲁棒控制

本文针对控制力矩陀螺框架伺服系统中存在的参数不确定性、摩擦非线性及外部干扰问题,提出了一种考虑LuGre摩擦的自适应鲁棒控制方法.针对陀螺框架伺服系统未知惯量和阻尼系数、LuGre摩擦参数不确定性及未知外部干扰上界,设计参数更新律对其进行估计.在此基础上,为提高系统对不确定参数及未知干扰的鲁棒性,设计带有期望补偿的自适应鲁棒控制器,可实现对LuGre摩擦非线性的精确补偿,同时减小测量信号噪声及外部干扰对系统的不利影响.应用Lyapunov稳定性理论分析了闭环系统的稳定性.对挠性航天器姿态机动控制的仿真结果,验证了所提方法的有效性.     

Neural network robust control of a 3-DOF hydraulic manipulator with asymptotic tracking

Multiaxial hydraulic manipulators are complicated systems with highly nonlinear dynamics and various modeling uncertainties, which hinders the development of high-performance controller. In this paper, a neural network feedforward with a robust integral of the sign of the error (RISE) feedback is proposed for high precise tracking control of hydraulic manipulator systems. The established nonlinear model takes three-axis dynamic coupling, hydraulic actuator dynamics, and nonlinear friction effects into consideration. A radial basis function neural network (RBFNN) is synthesized to approximate the uncertain system dynamics and external disturbance, which can greatly reduce the dependence on accurate system model. In addition, a continuous RISE feedback law is judiciously integrated to deal with the residual unknown dynamics. Since the major unknown dynamics can be estimated by the RBFNN and then compensated in the feedforward design, the high-gain feedback issue in RISE feedback control will be avoided. The proposed RISE-based neural network robust controller theoretically guarantees an excellent semi-global asymptotic stability. Comparative simulation is performed on a 3-DOF hydraulic manipulator, and the obtained results verify the effectiveness of the proposed controller.     

Analytical modeling and simulation of a 2-DOF drive and 1-DOF sense gyro-accelerometer

In this paper, we present a new analytical model for frequency as well as transient analysis of a 3-DOF gyro-accelerometer system having 2-DOF in drive and 1-DOF in sense direction respectively. The model constructs lumped parameter differential equations by vector analysis associated with each degree of freedom that comprises Coriolis action, Euler’s action and action due to external acceleration along with biasing counterparts. These coupled differential equations are then solved explicitly in the frequency domain by taking their Laplace transforms. Based on these formulations, a thorough system analysis has been carried out keeping in view the various parameters and issues related to the device design. Furthermore, a discriminating scheme for time varying angular rate and linear acceleration by combining the structural model of a gyro-accelerometer with the demodulation and filtering processes to investigate frequency response of a micro gyro-accelerometer has also been presented by taking into account the presently derived settled transient solution of sense mode response. Finally we have verified the present model with MATLAB Simulink, showing their excellent agreement with each other.     

Design of Optimal 2-DOF Sampled-Data Systems

A method is presented for synthesis of optimal sampled-data tracking systems with two controllers, one of which is incorporated into the closed loop, while another is placed in feedforward chain. The approach is based on Laplace transform in continuous time and polynomial equations theory. The set of all admissible reference controllers is constructed. The cost function include integral quadratic output and control errors in continuous time.     

Bulk micromachined tunneling tips integrated with positioning actuators

We have successfully developed an integrated micromechanical system for controlling tunneling current. A pair of nanoscale tunneling tips have been integrated with a silicon micromachined electrostatic actuator of high-aspect ratio. The tip sharpness has been observed to be as sharp as commercial tips by scanning over surface of carbon graphite as an atom scale. We have also succeeded to observe the tunneling current in the air and in the vacuum condition (in TEM).     

Linearization of electrostatically actuated surface micromachined2-D optical scanner

This paper presents an effective method of linearizing the electrostatic transfer characteristics of micromachined two-dimensional (2-D) scanners. The orthogonal scan angles of surface micromachined polysilicon scanner are controlled by using quadrant electrodes for electrostatic actuation. By using a pair of differential voltages over a bias voltage, we could improve the distortion of projected images from 72% to only 13%. A theoretical model has been developed to predict the angle-voltage transfer characteristics of the 2-D scanner. The simulation results agree very well with experimental data. Differential voltage operation has been found to suppress the crosstalk of two orthogonal scan axes by both experiment and theoretically. We have found that a circular mirror is expected to have the lowest angular distortion compared with square mirrors. Perfect grid scanning pattern of small distortion (0.33%) has been successfully obtained by predistorting the driving voltages after calibration     

Fabricating capacitive micromachined ultrasonic transducers with wafer-bonding technology

Introduces a new method for fabricating capacitive micromachined ultrasonic transducers (CMUTs) that uses a wafer bonding technique. The transducer membrane and cavity are defined on an SOI (silicon-on-insulator) wafer and on a prime wafer, respectively. Then, using silicon direct bonding in a vacuum environment, the two wafers are bonded together to form a transducer. This new technique, capable of fabricating large CMUTs, offers advantages over the traditionally micromachined CMUTs. First, forming a vacuum-sealed cavity is relatively easy since the wafer bonding is performed in a vacuum chamber. Second, this process enables better control over the gap height, making it possible to fabricate very small gaps (less than 0.1 /spl mu/m). Third, since the membrane is made of single crystal silicon, it is possible to predict and control the mechanical properties of the membrane to within 5%. Finally, the number of process steps involved in making a CMUT has been reduced from 22 to 15, shortening the device turn-around time. All of these advantages provide repeatable fabrication of CMUTs featuring predictable center frequency, bandwidth, and collapse voltage.     

A micromachined 2 /spl times/ 2 optical switch aligned with bevel-ended fibers for low return loss

This paper presents the design and optical performance characteristics of a micromachined 2 /spl times/ 2 optical switch with low return loss for an optical add-drop application. The switch is equipped with four optical fibers beveled at 8/spl deg/. An intentional lateral offset was introduced to align the refracted light at the input fiber-air interface with output fibers. A micromirror was actuated into the optical path by an electrostatic comb actuator to change the direction of the input optical signal. The optical switch was fabricated using silicon deep reactive ion etching (DRIE) of silicon-on-insulator (SOI) wafers. Optical performance measurements of the fabricated optical switch revealed that the time dependent loss (TDL), polarization dependent loss (PDL), and wavelength dependent loss (WDL) were -0.04 dB, -0.05 dB and -0.71 dB, respectively. The switching time was within 5 ms for a 24-V electrical step signal. Because the beveled ends of the optical fibers kept the propagated light from reflecting backward into the input fiber, the return losses were just -43 dB. This return loss was used to theoretically analyze a model of the beveled end by considering backscattering due to the surface roughness, which thereby was determined to be about 41 nm.     

Robust nonlinear control of a planar 2-DOF parallel manipulator with redundant actuation

A new robust nonlinear controller is presented and applied to a planar 2-DOF parallel manipulator with redundant actuation. The robust nonlinear controller is designed by combining the nonlinear PD (NPD) control with the robust dynamics compensation. The NPD control is used to eliminate the trajectory disturbances, unmodeled dynamics and nonlinear friction, and the robust control is used to restrain the model uncertainties of the parallel manipulator. The proposed controller is proven to guarantee the uniform ultimate boundedness of the closed-loop system by the Lyapunov theory. The trajectory tracking experiment with the robust nonlinear controller is implemented on an actual planar 2-DOF parallel manipulator with redundant actuation. The experimental results are compared with the augmented PD (APD) controller, and the proposed controller shows much better trajectory tracking accuracy.     

Innovative micromachined microwave switch with very low insertion loss

This work fabricates a novel type of micromachined microwave switch on a semi-insulating GaAs substrate using a microactuator and a coplanar waveguide (CPW) using electrostatic actuation as the switching mechanism. The microactuator uses several continuously-bent cantilevers connected in series. A cantilever with two sections, a straight-beam section and a curved-beam section, forms the basic unit of the microactuator. The straight-beam section is made of an aluminum (Al) layer, 0.5 μm thick. The curved-beam section is made of an Al layer of the same thickness, combined with a 0.1-μm layer of chromium (Cr) film. This section is initially curled due to the different residual stress of Al and Cr. The low temperature (250°C) process ensures that the switch is capable of monolithic integration with microwave and millimeter wave integrated circuits (MMIC). When no dc potential is applied, the actuator is curled far from the signal line of the CPW, and therefore the insertion loss at this `on' state is only 0.2 dB at 10 GHz. Because the metal microactuator is far from the signal line of the CPW at this `on' state, the microwave propagation is hardly disturbed by the microactuator. When an applied electrostatic force pulls the actuator tip down into contact with the signal line of the CPW, it creates a large capacitance between the actuator and the CPW. The isolation at this `off' state is −17 dB at 10 GHz. Maintaining the actuator in the `off' state requires only a very low actuation voltage of 26 V. Once the dc potential is removed, the residual stress of the actuator structure pulls it to the up position. The microactuator moving back and forth between these two switching states, acts like the movement of a frog's tongue. This switch has excellent performance at the wide-band RF frequencies used in transmit/receive modules of wireless communication. This study measured the critical corrupt (activating) voltage and recovery voltage of the microactuator. The 10-ms switching time of this switch is slower than the switching time of solid-state switches.     

Characterization of a high-sensitivity micromachined tunnelingaccelerometer with micro-g resolution

A new high-sensitivity bulk-silicon-micromachined tunneling accelerometer with micro-g resolution has been successfully fabricated and tested at Stanford University. This accelerometer is a prototype intended for underwater acoustics applications and is required to feature micro-g resolution at frequencies between 5 Hz and 1 kHz and can be packaged with circuitry in an 8-cm³ volume with a total mass of 8 g. This paper briefly describes the mechanical design of this tunneling accelerometer and focuses on the experiments carried out in our laboratory to test the tunneling transducer as well as on the experimental determination of accelerometer resolution. The exponential relationship between tunneling gap and tunneling current is verified and results in an effective tunneling barrier height of about 0.2 eV. The goal of this paper is to outline the measurements which are necessary to verify that the sensor is actually tunneling and to confirm that the accelerometer performance is consistent with what should be expected from a tunneling accelerometer     

Optical properties of surface micromachined mirrors with etch holes

We have investigated the optical properties of surface-micromachined polycrystalline silicon reflectors within the visible spectral range at five different wavelengths. The measurement results of the reflectivity of various microreflectors at four different incident angles (20°, 30°, 45°, and 60°) are presented. Optical properties of microreflectors realized using the multiuser MEMS process (MUMPS) have been investigated. Our studies have found that etch holes, widely used in the surface micromachining process to reduce the time for releasing structures by sacrificial undercutting, have a great influence on the optical properties of micromachined mirrors. Diffraction patterns created by two-dimensional etch-hole arrays on micromachined mirrors have been investigated. The diffraction by etch holes obeys the Fraunhofer diffraction theory when a collimated light source (e.g., a laser beam) is incident. We have shown that when the dimension of etch holes increases, an increasing portion of the incident power will be diffracted and transmitted due to etch holes, leading to decreasing reflectivity of surface micromachined mirrors     

基于DSP的控制驱动一体化二自由度机器人云台设计

本文提出了一种二自由度机器人云台的设计方案，详细阐述了该方案的硬件和软件设计。本方案选用DSP作为主控芯片，两相混合式步进电机作为执行机构，硬件电路采用控制驱动一体化设计。实验结果证明，云台具有结构简单、体积小、调速范围广、定位精度高等优点。